Optical see-through (OST) displays allow users to view digital content and physical objects simultaneously. They come in multiple form factors (e.g. head mounted displays, projection-based and transparent LCD and OLEDs) and are widely used in augmented reality (AR) applications including medical, maintenance, education and training (see [Bimber and Raskar 2005][Carmigniani et al. 2011] for a comprehensive list of applications). OST displays can be additive (have their own light source e.g. projection-based displays or transparent OLED) or subtractive (filter white light from an external source e.g. LCD). With a few consumer electronics starting to adopt them [Lenovo 2013][Epson 2013] and the continuous development of transparent OLED (Futaba Corporation [link], Fujitsu [link], Winstar [link]) and LCD displays (Samsung NL22B [link], Eyevis [link]) we expect they will be widely available.
An important aspect of additive OST displays is that light coming from real-world objects mixes with the light emitted by the display: also known as color blending [Gabbard et al. 2010]. Color blending is an important issue as it affects the legibility and color—encodings of digital information and compromises the general us—ability of such devices. Existing solutions include using a spatial light modulator (SLM) to block background light [Kiyokawa et al. 2002][2003], an approach requiring extra hardware on the display at the cost of non-transparency. Color correction is another solution where the system finds an alternative digital color which, upon blending with the background, comes closest to the desired color [Weilland et al. 2009].
The perception of color as a blend of the display color and the background [4] can be a major usability problem in optical head-mounted displays (OHMD). For example, users perceive red as magenta when the background is blue, and as yellow when the background is green. Color blending has several negative effects on the display content it reduces the readability of text [18], makes augmented reality (AR) objects look translucent and unreal [1], Impairs the interpretation of color-encoded information such as status icons or system alerts, and leads users to confusion [19]. Therefore, addressing color blending is an important issue as it compromises the usability and adoption of OHMDs [10][11].
Existing solutions to color blending include occlusion support and color correction. The occlusion approach uses spatial light modulators such as liquid crystals to block light coming from the background and keep it from blending with the display color [3]. Occlusion support requires additional optical hardware, making the OHMD bulky [3][5] and compromising its transparency [14]. The color correction approach consists on determining an alternative color which, upon blending with the background, results on a color closer to the one originally designed for. Color correction does not require additional optical hardware and therefore does not affect the overall transparency and lightness of the display. However, existing color correction algorithms are not usable. Weiland et al. proposed several correction algorithms which often result on black or depend on arbitrary constants [24].